ISBN also called I.S.B.N. stands for International Standard Book Number. Any book which is published must have ISBN, it is a unique machine-readable identification number, which marks any book unmistakably. This number is defined in ISO Standard 2108. The number has been in use now for 35 years and has revolutionised the international book-trade. 170 countries and territories are officially ISBN members. The ISBN accompanies a publication from its production onwards.